Growlers are generally made of glass and have either a screw-on cap or a hinged porcelain gasket cap, which can maintain freshness for a week or more.
A properly sealed growler will hold carbonation indefinitely and store beer like any other sanitized bottle.
Some growler caps are equipped with valves to allow replacement of carbon dioxide lost while racking.
The modern glass growler was first introduced by Charlie and Ernie Otto of Otto Brothers' Brewing Company in Wilson, Wyoming, in 1989.
The two most popular colors for growlers are amber (a brownish hue) or clear (often called "flint").
Clear growlers are often 25% to 35% more per unit than their amber counterparts.
Glass handles are the most common type of handle for growlers, although metal handles, with more ornate designs, can also be found.
Some growlers do not have handles; this is especially common with smaller growlers.